Japanese Laid-Open Patent Publication No. 2001-236848 describes a switch device including a plurality of switches like a combination switch for a vehicle. The switch device is connected by a cable to a controller. An information signal related to the activation and deactivation of a switch is sent through the cable to the controller.
There are two types of such a switch device, a non-multiplex type and a multiplex type. A non-multiplex type switch device includes connector terminals, the number of which is greater than or equal to the number of the switched. Voltage is applied to each connector terminal in accordance with the activation state or deactivation state of the corresponding switch. A signal line is provided for each switch. Thus, the number of signal lines arranged in the cable is the same as the number of switches.
FIG. 4A shows a multiplex type switch device. The switch device includes an integrated circuit (IC) 100. The IC includes IC terminals 101 connected by connecting members 103 to contacts 105a to 105h or connector terminals 102a to 102c. The connector terminal 102a is a communication connector terminal, and the two connector terminals 102b and 102c are power connector terminals.
Voltages corresponding to an activation or deactivation state of switches are applied to the contacts 105a to 105h, and consequently, to the connecting members 103 and the IC terminals 101 that are connected to the contacts 105a to 105h. Operational power is supplied by the power connector terminals 102b and 102c to the IC 100. Based on the voltages applied to the contacts 105a to 105h, the IC 100 outputs an information signal related to the activation and deactivation state of the switches to the communication connector terminal 102a. The information signal is then sent through a cable from the communication connector terminal 102a to a controller (not shown). In this manner, in a multiplex type switch device, the number of connector terminals and the number of signal lines in the cable can be reduced.
However, in the structure of FIG. 4A, the connecting members 103 are required to be laid out without contacting one another from the IC terminals 101 to the contacts 105a to 105h. This results in the switch device having a complicated internal structure.
Further, as shown in the enlarged view of FIG. 4B, in the IC 100, for example, an IC terminal 101a, which is supplied with power and connected to the power connector terminal 102b or 102c, may be arranged adjacent to an IC terminal 101b, which receives voltage that is in accordance with the activation or deactivation state of a switch and connected to one of the contacts 105a to 105f. The voltage applied to the IC terminals 101a is higher than that applied to the IC terminal 101b. Thus, the magnetic field formed by the IC terminal 101a may influence and change the voltage level of the adjacent IC terminal 101b. Accordingly, to reduce the influence of the magnetic field formed by the IC terminal 101a, a protection element such as a capacitor must be provided for the IC terminal. The IC terminal 101b may be influenced by such a magnetic field not only when the IC terminals 101a and 101b are arranged adjacent to each other but also when the distance between the IC terminals 101a and 101b is short.